1. Field of the Invention
The present invention relates to a laser processing apparatus for performing laser processing to a workpiece such as a semiconductor wafer.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby partition a plurality of regions where a plurality of devices such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the streets to thereby divide the regions where the devices are formed from each other, thus obtaining a plurality of individual semiconductor chips. Further, an optical device wafer is provided by forming a plurality of optical devices including light receiving devices such as photodiodes and light emitting devices such as laser diodes on the front side of a sapphire substrate. The optical device wafer is also cut along the streets to obtain the individual optical devices divided from each other, such as photodiodes and laser diodes, which are widely used in electric equipment.
As a method of dividing a wafer such as a semiconductor wafer and an optical device wafer along the streets, there has been proposed a method of applying a pulsed laser beam along the streets to thereby form laser processed grooves along the streets on the wafer and next breaking the wafer along these laser processed grooves.
However, when a laser beam is applied to a wafer of silicon, sapphire, etc. as a workpiece along the streets, the wafer is melted to cause scattering of melt dust, or debris, so that there arises a problem such that the dust scattered may stick to the front side of the devices formed in the rectangular regions of the wafer, causing a degradation in quality of each device. Further, there is another problem such that the dust such as debris scattered may stick to a focusing lens included in focusing means for applying a laser beam, causing the interference with the application of the laser beam.
To solve this problem, there has been proposed a laser processing apparatus including dust discharging means for collecting and discharging dust such as debris generated by the application of a laser beam to a workpiece from focusing means constituting laser beam applying means (see Japanese Patent Laid-open No. 2007-69249, for example).